Oxidation, of ammonium

Another important greenhouse gas is a product of phytoplankton oxidation of ammonium. This reaction can follow two pathways ... 

Autotroph Organism which uses carbon dioxide as the sole carbon source. Autotrophic nitrification Oxidation of ammonium to nitrate through the combined... 

Nitrification consists of two energy yielding steps the oxidation of ammonium to nitrite, and the oxidation of nitrite to nitrate. These equations are generally represented as follows ... 

Recent research has identified some other microbial routes for denitrification that are not heterotrophic. One, called the anammox reaction, involves the oxidation of ammonium to N2 using either nitrite or nitrate as the electron donor. The second has bacteria using Mn " to reduce nitrate to N2. As noted earlier, N2 is generated by the oxidation of ammonium using Mn02 as the electron acceptor. [Denitrification may also be supported by Fe " (aq) oxidation.] These reactions are summarized in Table 12.2. The overall consequence of these reactions is that ammonium does not accumulate in the pore waters where Mn respiration and denitrification are occurring. 

In oxic seawater, chemoautolithotrophic bacteria of the family Nitrobacteraceae mediate the stepwise oxidation of ammonium to nitrite and then to nitrate. This process is... 

Figure 18-19 The ammonia oxidation system of the bacterium Nitrosomonas. Oxidation of ammonium ion (as free NH3) according to Eq. 18-17 is catalyzed hy two enzymes. The location of ammonia monooxygenase (step a) is uncertain but hydroxylamine oxidoreductase (step b) is periplas-mic. The membrane components resemble complexes I, III, and IV of the mitochondrial respiratory chain (Fig. 18-5) and are assumed to have similar proton pumps. Solid green lines trace the flow of electrons in the energy-producing reactions. This includes flow of electrons to the ammonia monoxygenase. Complexes HI and IV pump protons out but complex I catalyzes reverse electron transport for a fraction of the electrons from hydroxylamine oxidoreductase to NAD+. Modified from Blaut and Gottschalk.315...

The first reaction is slower than the second one, so the resulting effluent nitrite concentration will be small. Nitrate is the final oxidation state if no denitrification takes place in the aerator. In the oxidation of ammonium nitrogen alcalinity is lost. About half of it could be restored if the system is designed for denitrification as well. 

Nitrification is carried out by unique specialized bacteria in a two-step reaction. The first step, oxidation of ammonium (NH4) to nitrite (NOp, is catalyzed by a few species of bacteria that have names beginning with nitroso-, for example, nitrosomonas and nitrosospira. The reaction is as follows ... 

Various soil processes also contribute to soil acidity. Decaying organic matter releases a number of organic acids, as indeed do plant roots. Nitrification, the microbial oxidation of ammonium ions to nitrate by Nitrosomonas and Nitrobacter, occurs in slightly acidic to neutral soils and releases H" " ions ... 

Another anaerobic process that removes bio-available nitrogen from the water is the anaerobic oxidation of ammonium (Anammox), in which ammonium and nitrite are combined to form N2, thus... 

Ward, B. B. (1990). Relationship between substrate concentration and oxidation of ammonium and methane in a stratified water column. Continental Shelf Research 12, 1193—1208. 

A more easily filtered product is obtained by using aqua regia than by using chlorine. water. For the same reason the product is allowed to precipitate slowly from a hot solution. Thorough removal of aqua regia by boiling prevents oxidation of ammonium ion in the next step. 

Nitrate is synthesized from ammonium by an important bacterial process known as nitrification. The first step in nitrification is the oxidation of ammonium to nitrite (NO 2"), a function carried out by bacteria in the genus Nitrosomonas. Once formed, the nitrite is rapidly oxidized further to nitrate, by bacteria in the genus Ni-trobacter. The bacteria responsible for nitrification are very sensitive to acidity, so this process does not occur at significant rates in acidic soil or water. This is the reason why plants of acidic habitats must be capable of utilizing ammonium as their source of nitrogen nutrition. 

Most nitrous oxide produced in terrestrial and aquatic ecosystems is associated with the processes of nitrification and denitrification. Nitrification is the oxidation of ammonium (NH4) to nitrate, and is carried out by chemoautotro-phic bacteria in oxygenated environments, where ammonium is present (Haynes, 1986) ... 

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